Hi Bryan [quote userid="204916" url="~/support/data-converters-group/data-converters/f/data-converters-forum/1492482/ads1235-inconsistent-measurement-drift-and-step-changes-in-strain-gauge-system/5738143#5738143"]It does seem like sensor is adding an error to your system, the plot where you are just measuring a resistor divider looks much cleaner (can you use the same units for all plots however? Some have a y-axis in volts, some in codes, it will be easier to compare if they are all the same. Codes should be fine)[/quote] Both have the same units—Codes. The thing is that the measurements with the sensors range from approximately 100K to 300K Codes, while those with the resistors are in the order of millions of Codes. To improve the readability, the latter plot is scaled by applying a factor of 1e6 (as indicated in the upper left corner of the plot). I realize the font size is quite small—I’ll make it larger next time for better clarity. [quote userid="204916" url="~/support/data-converters-group/data-converters/f/data-converters-forum/1492482/ads1235-inconsistent-measurement-drift-and-step-changes-in-strain-gauge-system/5738143#5738143"]Can you explain your reference circuit to me? The schematic shows what looks like a true ratiometric reference on REFP0 and REFN0, where the bridge excitation voltage is directly used as the ADC reference voltage. I am not sure what the VREF- net is however, as this appears to be grounded.[/quote] I based my design on the typical application circuit from the ADS1235 datasheet. In my implementation, Exc+ and Sen+ are the same wire (labeled as V_Left+ for one ADC and V_Right+ for the other). Each sensor is powered through an eFuse, that's why there are 2 Exc+ lines (V_Left+ and V_Right+). Similarly, Exc- and Sen- are the same wire and are grounded at the PCB. I made this design choice to simplify wiring and reduce costs by using smaller connectors and fewer wires, given that each PCB measures 2 sensors. I assumed this would come with the following trade-offs: Increased noise in the measurements: However, based on field data, the measured deformations are significantly larger than the noise, making the added noise acceptable. Voltage drop across the cable: I expect this drop to be small and stable. Any offset introduced by it can be calibrated at the start of the operation. Maybe I'm wrong on this one, but I don't see how this could be related to the step change or drift issues I'm observing, especially the step changes, which also appeared when measuring the fixed resistor divider with very short wiring. [quote userid="204916" url="~/support/data-converters-group/data-converters/f/data-converters-forum/1492482/ads1235-inconsistent-measurement-drift-and-step-changes-in-strain-gauge-system/5738143#5738143"]However, you have said that you are using a resistor divider for your reference, which I assume is the one shown in the bottom of the image below. It is not clear to me why would you use a resistor divider instead of the ratiometric reference, or why you have both. And are those matched resistors, or just two discrete components?[/quote] You are right, it’s the resistor divider shown in the image you attached. They are 2 discrete resistors with 0.1% tolerance, though you are right that using matched resistor could improve performance. We included the resistor divider because the deformation we’re measuring is complex, and we need to individually assess how each strain gauge deforms. Isn't my measure still ratiometric? Both the resistor divider and the strain gauges form a Wheatstone bridge, only that each adjacent arm is located in a different place, but they are excited from the same source. I appreciate your support! Best regards, Edgar
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